If 2^-n = x, find 2ⁿ.

We are given the equation:

$$2^{-n} = x$$

The rule of negative exponents states that $a^{-b} = \frac{1}{a^b}$.
Applying this rule to $2^{-n}$:

$$2^{-n} = \frac{1}{2^n}$$

Now we have:

$$\frac{1}{2^n} = x$$

To find $2^n$, we can take the reciprocal of both sides of the equation:

$$\frac{1}{\left(\frac{1}{2^n}\right)} = \frac{1}{x}$$ $$2^n = \frac{1}{x}$$

The value of $2^n$ is $\frac{1}{x}$.

The correct option is D.

$\boxed{\text{D. } \frac{1}{x}}$